Blade element momentum theory for a skewed coaxial turbine

A coaxial turbine under skew with significant rotor spacing has the potential for increased power output compared to a flow-aligned turbine due to a portion of the downstream rotor experiencing freestream velocity, referred to as a fresh flow region. A lab-scale prototype was designed and built to investigate the skew-to-power relationship of a coaxial turbine system as it compared to a blade element momentum theory model with multiple, sheared streamtubes representing the downstream rotor fresh flow region. The inclusion of the downstream rotor fresh flow region in the theoretical analysis is compared to the experimental data. The results support that the torque and power performance of the downstream rotor and overall skewed coaxial turbine system are predicted more accurately.